It is common practice in the petroleum industry to employ gases such as CO.sub.2 or N.sub.2 in stimulation and treatment of oil and gas wells, such as in acidizing, fracturing, well cleanout or CO.sub.2 flooding. In addition, such a gas may be employed in foaming cement to be employed in cementing operations in a well bore. The gas is transported in low temperature liquified form to the well site in insulated tank trailers, where it is introduced into the suctions of one or more positive displacement pumps (generally referred to as the "primary" pumps) in order to increase the pressure of the liquified gas prior to mixing with cement or a primary treating fluid which may carry various additives. If well treatment involves fracturing the producing formations in the well, the treating fluid may also carry proppants to prevent formation closure after fracturing. The CO.sub.2 or N.sub.2 provides a gaseous phase in the treating fluid upon increase in temperature and decrease in pressure in the formation, which gas is highly beneficial to the treatment in that it reduces the amount of treating fluid and additives required, provides a light weight carrier medium for proppants, and places less stress on the producing formation than a heavier, unfoamed treating fluid. In a similar manner, foamed cement is employed when a heavier cement may be deleterious to the producing formations. This latter effect is of particular concern in gas wells, where the formations may be physically weak and susceptible to collapse under the weight of a column of unfoamed treating fluid or cement.
Recently, methods have been developed to stimulate wells employing CO.sub.2 as the primary treating fluid, with a relatively small proportion of another liquid or gel employed to transport additives or support proppants.
The prior art layout of equipment employed in operations such as are described above requires the use of a centrifugal or vane type booster pump and preferably a liquid/gas separator between the liquified gas tank and a primary pump. This equipment is required due to the heat gain in the line leading to the primary pump, which heat gain induces vapor lock in the line and prevents proper liquid intake into the primary pump, causing cavitation in the fluid end thereof and possible destruction of the pump itself. The vaporization problem increases as the gas is emptied from the tank, as the tank pressure drops with a consequential tendency toward vapor lock. The aforementioned booster pump and separator necessitates at least one additional trailer on site, as well as constant monitoring of the booster pump and a fairly high level of maintenance between jobs. On large jobs, several booster pump trailers may be required. In addition, the prior art booster pump becomes less effective at high tank pressures due to increased tendency of the fluid to form vapor.